What Causes Changes in Motion?

Personal Lab 1

Background

Motion is such an ingrained part of our daily lives that we rarely pause to contemplate it. We rarely notice the more subtle details of the motions of objects around us. Objects which move horizontally can roll, slide or move through the air. Where can we find examples in nature of horizontal motions? Liquids can move through pipes that are laid out horizontally. Winds in stormy weather can blow in a horizontal direction. A train traveling across a flat terrain moves horizontally. A hockey puck swiftly and easily slides in a horizontal path across an ice rink. The conveyor belt carries groceries in a horizontal path toward the clerk in the supermarket. An airliner flies with a horizontal motion when crossing the country at an altitude of 35,000 feet. What causes motion? And what causes changes in motion?

Purpose

To investigate the motions of objects on flat, horizontal surfaces.

To study the factors that influence an object’s vertical motion when dropped.

Materials

Balls, 1" diameter, steel (1), glass (1)	Paper, 2 sheets, 8.5" x 11"
Coffee Filter	Textbook

Procedure

1. Locate a large, flat table or desk top with a smooth surface. Spend a moment observing the motion of each ball, after you simply place it on the horizontal surface. Record your observations.

2. Give one of the balls a very slight tap, and carefully observe the motion that results. Record your observations.
Repeat the experiments in a variety of ways, so that you become certain of any patterns or trends that you observe in the horizontal motions. Are the motions of the balls constant after you tap them? Or does the motion change after you tap the ball? If so, how and why?

3. Is there any difference in the motion of a ball when you tap it compared to continuously pushing the ball along the table top? Do this experiment and record your observations.

4. What happens to the ball’s motion when it rolls off the edge of the table? List all the ways the ball’s motion changes.

Below is an example of a Data Table you might construct to record your observations in your Lab Book:

Data Table 1: Motions of Rolling Balls

Exp#	Object	Action Applied to Ball	Predicted Motion	Observed Path of Motion (curved, straight line path, etc...)	Observed Speed (constant, increasing, etc...)
1	steel ball	slight tap	ball will roll in curved path at non-con- stant speed	etc...	etc...
2	steel ball	continuous push		etc...
3	glass ball	slight tap		etc...
4	glass ball	continuous push		etc...
5	drop	etc...
6	book	etc...
7	sheet of paper	etc...

5. Perform separate experiments to determine the factors that influence the "free-fall" times of pairs of balls dropped simultaneously to the ground. Predict which ball will reach the ground first if both balls are released simultaneously. Check your predictions with the balls in your Science Kit. [Note: "free-fall" is motion that results when an object is dropped and falls freely to the ground.]

6. To probe "free-fall" more thoroughly, perform an experiment by dropping a sheet of paper and a text book simultaneously. You might try, for example, dropping the book with the sheet of paper resting on top, and with the paper below the book. In each case make predictions for the separate motions of the paper and the book before you perform the experiment.

7. Perform another experiment in which you crumple one of the sheets of paper into a ball and drop it simultaneously with the book. Also try dropping the crumpled paper simultaneously with an "uncrumpled" sheet of paper. Before doing each of these experiments, make predictions about what you expect to happen. Record your predictions, and your observations in the Data Table in your Lab Book.

8. Observe the motion of the coffee filter when dropped from a height of at least one meter above the ground.

Questions

Hand in your Data Table, and your notes on observations made in procedures 5)-8) together with sketches of the following four graphs. Be sure to label each graph clearly.:

1. Sketch a graph of position vs. time for a ball moving across a horizontal, frictionless surface after being given a slight tap.

2. Sketch the graph of speed vs. time for the ball in 1).

3. Sketch a graph of position vs. time for a ball which is pushed continuously across a horizontal table top. (Again ignore the effects of friction.)

4. Sketch a graph of speed vs. time for the ball in 3).